I don't know if it is possible to get the cookie and attach the session ids to the request using rewrite_mod in an Apache2 server. I am using one to create redirections to use friendly urls to the contents.

This would be a workaround and not a solution, but could you link to another page that doesn't throw the error (thus setting the cookies) and then redirect to the proper page? Or does the error come up on EVERY public page?

I know this is an old topic, but for anyone who is trying to figure out how to create a direct url to something that Blackboard doesn't appreciate (3rd party tool, protected content, etc), you can use the following:

<school url>/webapps/login/?action=default_login&new_loc=<uri encoded location starting with %2Fwebapps, not the full url>

SSO should work with this url, and if not, it will prompt the user to login and send them on their way.